1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a fast adaptive time domain equalizer for a Time Reversal-Space Time Block Code (TR-STBC) system.
2. Description of Related Art
The reliability of wireless systems may be improved by using diversity techniques, combined with an equalizer, at a receiver and are to reduce an Inter-Symbol Interference (ISI) caused by a multipath propagation.
A Time Reversal-Space Time Block Code (TR-STBC), which generalizes a STBC method to a frequency selective channel, is known as an efficient transmit diversity technique.
An optimal equalizer for a TR-STBC-based transceiver is a maximum likelihood sequence estimator implemented using a Viterbi algorithm.
However, a Viterbi equalizer may not be implemented in real-time due to the exponential increase in complexity caused by a signal size, the number of antennas, and the length of channel impulse response.
Accordingly, as alternatives, an adaptive Decision Feedback Equalizer (DFE) is considered. Such a DFE requires only linear processing complexity while maintaining an excellent performance.
As a method of removing an ISI from two output streams of a 2×1 TR-STBC decoder, a method of using two single-input single-output (SISO) DFEs, which are independently adapted in parallel, is used.
FIG. 1 is a diagram illustrating a configuration of a 2×1 TR-STBC system using two SISO DFEs independently adapted in parallel in a conventional art.
Two output streams, that is, z1(t) and z2(t), which are outputted from a TR-STBC decoder 101 to a first SISO DFE 102A and a second SISO DFE 102B have the same second-order statistics. However, since the first SISO DFE 102A and the second SISO DFE 102B are independently adapted in parallel, the first SISO DFE 102A and the second SISO DFE 102B are uncoupled in terms of input signal statistics.
Also, in the configuration of the equalizer in the conventional art, general algorithms such as a Least Mean Square (LMS) algorithm, a normalized LMS (NLMS) algorithm, a Recursive Least Square (RLS) algorithm, and the like, are used to update tap weights of the equalizer.
However, in the above algorithms in the conventional art, a convergence speed is slow, a long training sequence is required to track a time-varying wireless channel, and a bandwidth efficiency of system is reduced.
Thus, a fast adaptive time domain equalizer for a TR-STBC system is required.